| Project
Title: |
The
improvement of Australian tea tree through selection and breeding (continuation
of project DAN-87A) |
| RIRDC
Project No.: |
DAN-151A |
| Researcher: |
Dr
Ian Southwell |
| Organisation: |
NSW
Agriculture
Wollongbar Agricultural
Institute
Wollongbar NSW 2477 |
| Phone: |
02
66261224 |
| Fax: |
02
66283264 |
| Email: |
ian.southwell@agric.nsw.gov.au |
| Objectives |
To
systematically improve the yield and quality of oil from tea tree (Melaleuca
alternifolia) by:
· Continuing current
and establishing new selection trials.
· Production of improved
seed lines with yields up to 17% higher than current industry selections
by 1997, 30% higher by 2000 and 60% higher by 2003.
|
| Background |
The
Australian tea tree oil industry has developed from bush production to
plantation production. Currently, productivity in the industry is considered
below potential. A contributing factor is seed quality, as plantations
are established largely from seed collected from a limited number of bush
trees with only rudimentary selection. Clearly, any gains a breeding program
could achieve in oil quality and productivity would assist the local industry
in maintaining its international competitiveness. |
| Research |
During
the eight years of consecutive projects (1993-2001), multiple field trials
were established to determine variability in and genetic parameters for
oil yield and quality. One of these trials was progressively culled of
inferior trees to become a seedling seed orchard which produced the first
improved seed in 1999. Controlled pollination techniques have been developed
and employed in nucleus breeding and production of hybrids. Research in
these and related projects has provided methods for DNA fingerprinting
of breeding lines and demonstrated the potential of clonal plantations.
A second-generation seedling seed orchard was established in 2001. |
| Outcomes |
The
breeding project has distributed 7kg of seed to industry, enough to plant
over 1000ha of tea tree plantation, in four releases since 1997. Most of
this seed has been from the best natural provenances capable of providing
20% improvement in yield over industry standards, as demonstrated by project
yield trials. Seed from the seedling seed orchard and a clonal seed orchard
was released for the first time in 2000. A 30% increase in yield is predicted
through use of this seed and further culling of the orchard during 2000
is expected to give improvements of 60% by 2003. |
| Implications |
A
very favourable outcome from past investment in the breeding program has
been demonstrated by several financial analyses. The gains provided by
the tea tree breeding project are a vital part of ensuring the economic
viability of the industry in Australia. |
| Publications |
Baker,
G. (1999). Tea tree breeding. Pages 135-151 in Southwell I and Lowe
R eds., Tea Tree: The Genus
Melaleuca. In Medicinal and Aromatic
Plants – Industrial Profiles, Hardman R ed. Vol. 9. Hardwood Academic Publishers:
The Netherlands.
Baker, G. and Doran, J. (1999).
Breeding Melaleuca alternifolia for essential oils. Proceedings
11th Australian Plant Breeding Conference, Adelaide. Vol. 2,
pp. 104-105.
Baker, G.R., Lowe, R.F. and
Southwell, I.A. (2000). Comparison of oil recovered from tea tree leaf
by ethanol extraction and steam distillation. J.Ag..Food Chem. 48:4041-43.
Doran, J. and Baker, G. (2000).
Using clones to establish tea tree plantations. The Short Report No. 73.
RIRDC: Canberra.
Doran, J.C., Baker, G.R.,
Murtagh, G.J. and Southwell, I.A. (1997). Improving tea tree yield and
quality through breeding and selection. RIRDC Res. Paper Series No 97/53. |
|
Project
Title:
|
The
anti- inflammatory activity of tea tree oil –second stage
|
|
RIRDC Project No.:
|
UF-5A |
|
Researcher:
|
Prof.
John Finlay-Jones Dr Prue Hart |
|
Organisation:
|
Flinders
University |
|
Phone:
|
08
8201 3909 08 8204 5404 |
|
Fax:
|
08
8201 3905 08 8276 8658 |
|
Email:
|
John.finlay-jones@flinders.edu.au
prue.hart@flinders.edu.au |
|
Objective
|
To
assess the anti-inflammatory activity of tea tree oil, and its components. |
|
Background
|
The
anti-bacterial, anti-viral and anti-fungal properties of tea tree oil have
been well studied. However, reports that tea tree oil has anti-inflammatory
properties have, until recently, been anecdotal. This laboratory has considerable
experience in determining the anti-inflammatory properties of cytokines,
in particular, interleukin-4 in vitro. |
|
Research
|
In
the first study, blood monocytes (>90% enriched by centrifugal elutriation)
were stimulated in vitro for 24 and 48 hours with a potent activating
agent, lipopolysaccharide. In response, the monocytes produced large amounts
of mediators that have been well characterised to initiate and sustain
inflammation. The effect of co-incubation with tea tree oil, and its water
soluble components, was investigated. In the second study, both monocytes
and neutrophils were isolated from blood and activated in vitro
to give a respiratory burst, the products of which can oxidise and damage
body tissues. The effect of tea tree oil on the production of a respiratory
burst induced by multiple stimuli was examined. |
|
Outcomes
|
Tea
tree oil was toxic to monocytes and neutrophils at concentrations >0.016%.
However, the water-soluble components (terpinen-4-ol (42%), ?-terpineol
(3%), 1,8-cineole (2%, respectively, of tea tree oil)) were not toxic and
suppressed inflammatory mediator production by activated monocytes. Terpinen-4-ol
was responsible for this activity. Neutrophils were unresponsive to tea
tree oil or any of its water soluble components for modulation of a respiratory
burst. In contrast, both terpinen-4-ol and ?-terpineol suppressed a respiratory
burst in activated monocytes. |
|
Implications
|
There
was selective regulation of monocyte, not neutrophil, inflammatory activity.
These results suggest that tea tree oil may enable neutrophils to be fully
active in an acute inflammatory response and eliminate foreign antigens,
while suppressing monocyte inflammatory mediator and superoxide production
and thereby preventing oxidative tissue damage that may be seen in more
chronic inflammatory states. These studies demonstrate the potential of
tea tree oil as a safe, topical, anti-inflammatory therapeutic agent. However,
as we are uncertain of the concentrations of terpinen-4-ol and ?-terpineol
that may penetrate beyond the stratum corneum. These results require documentation
of a reduction of inflammatory cells and mediators in skin after application
of tea tree oil. |
|
Publications
|
Hart
PH, C Brand, CF Carson, TV Riley, RH Prager, JJ Finlay-Jones. 2000. Terpinen-4-ol,
the main component of the essential oil of Melaleuca alternifolia
(tea tree oil), suppresses inflammatory mediator production by activated
human monocytes. Inflammation Research (in press).
Brand C, A Ferrante, RH Prager,
TV Riley, CF Carson, JJ Finlay-Jones, PH Hart. 2000. The water-soluble
components of the essential oil of Melaleuca alternifolia (tea tree
oil) suppress the production of superoxide by human monocytes, but not
neutrophils, activated in vitro. Inflammation Research (submitted). |
|
Project
Title:
|
Tea
Tree Oil as a topical decolonisation agent for adult inpatients with Methicillin-Resistant
Staphylococcus
aureus |
|
RIRDC Project No.:
|
UNC-7A |
|
Researcher:
|
Dr
John Attia |
|
Organisation:
|
University
of Newcastle
Centre for Clinical Epidemiology
& Biostatistics
University Drive, Callaghan,
NSW, 2308
AUSTRALIA |
|
Phone:
|
02
4923 6142 |
|
Fax:
|
02
4923 6148 |
|
Objective
|
To
find out if a body gel with Tea Tree Oil and a nasal ointment containing
Tea Tree Oil can be used in the hospital to help people get rid of "golden
staph" (MRSA) from their skin and in their nose. |
|
Background
|
MRSA
is a big infection control problem in Australian hospitals. Concerns primarily
focus on the spread of MRSA and the complications from the infection. We
are running out of antibiotics to treat MRSA infections. The application
of a topical antimicrobial body wash solution is currently recommended
for the control of MRSA within the health care setting. Success rates with
the current body wash (soaps) solutions are not consistent and we need
a more effective solution. Laboratory studies suggest Tea Tree Oil (TTO)
may be useful in the treatment of MRSA. MRSA is found to die in the presence
of TTO in the laboratory setting. Research is needed to see if this is
indeed true. |
|
Research
|
This
study design, a randomised-controlled trial, is the best sort of study
to find out if the tea tree oil products will work in the hospital setting.
Work carried out in the laboratory suggests the tea tree oil products should
work in the hospital setting. This is the research ever trying to find
out the answer to this question. |
|
Outcomes
|
The
main reason for doing this study is to find out if the results of the work
done in the laboratory can applied to the hospital setting. The main outcome
of the study is to clear patients of golden staph carriage in the hospital
– we do this by substituting the products we would normally use with the
tea tree oil products and then compare the number of times we get rid of
the golden staph. |
|
Implications
|
If
this is found to work the industry here in Australia can look to get the
tea tree oil products registered for use in the clinical setting and provide
us with a natural alternative to the man-made antibiotics we would normally
use. |
|
Publications
|
Articles
providing results of the studies undertaken to date have been presented
or published in the scientific literature (journal) and at international
meetings.
· A randomised-controlled
trial to determine the clinical efficacy of Tea Tree Oil as an alternative
topical decolonisation agent for adult inpatients with MRSA
Poster presented at the 3rd
Hospital Infection Society International Conference, Edinburgh September
1998
· Tea Tree Oil as
an Alternative Topical Decolonisation Agent for Methicillin-Resistant StaphylococcusAureus
Paper presented NSW Infection
Control Conference, Batemans Bay October 1999
· A randomised-controlled
trial to determine the clinical efficacy of Tea Tree Oil as an alternative
topical decolonisation agent for adult inpatients with MRSA
Poster presented at the 4th
Decennial International Conference on Nosocomial and HealthCare-Associated
Infections, Atlanta March 2000
· Caelli M. Porteous
J. Heller R. Riley T. Tea Tree Oil as an alternative topical decolonisation
agent for methicillin-resistant Staphylococcus aureus. Journal of
Hospital Infection 46 (3): 236-237, 2000 Dec.
|
|
Project
Title:
|
The
antiviral activity of tea tree oil in vitro |
|
RIRDC Project No.:
|
UWA-40A |
|
Researcher:
|
A/Prof
T. Riley |
|
Organisation:
|
University
of Western Australia
Dept of Microbiology
Queen Elizabeth II Medical
Centre
Nedlands WA 6009 |
|
Phone:
|
08
9346 3690 |
|
Fax:
|
08
9346 2912 |
|
Email:
|
triley@cyllene.uwa.edu.au |
|
Objective
|
The
aim of this project is to develop and validate methods suitable for testing
the antiviral activity of tea tree oil in vitro and to use these
methods to assess its potential as a topical antiviral therapeutic agent.
The outcomes will be the development of methods, the validation of these
methods and an assessment of the suitability of tea tree as a topical antiviral
agent. |
|
Background
|
A
critically important element of tea tree oil’s success in recent years
has been the scientific substantiation of claims regarding its antiseptic
and disinfectant capacity. Scientifically valid data demonstrating the
ability of tea tree oil to inhibit a wide range of bacteria and fungi have
increased its acceptability as a naturally-occurring antimicrobial agent,
both nationally and internationally. Despite significant anecdotal evidence
suggesting that tea tree oil is useful in the topical treatment of some
viral infections, such as coldsores, antiviral activity had not been proven
scientifically. Without data indicating that tea tree oil has antiviral
activity, there was no sound basis for in vivo clinical trials.
Without the support of results from clinical trials, tea tree oil is unlikely
to be accepted as an antiviral agent. Consequently, as the first step in
validating its use in treating viral infections, there was a need for basic
in
vitro susceptibility data. |
|
Research
|
Cell
culture methods were used to assess the in vitro antiviral activity
of tea tree oil. Briefly, in these methods, cultures of virus were prepared
in monolayers of cell culture, treated with tea tree oil and the effect
of tea tree oil addition on the virus determined. The activity of tea tree
oil against herpes simplex virus was determined in this manner. In addition
to providing data on the susceptibility of viruses to tea tree oil, the
tests also provided information regarding the toxicity of tea tree oil
in human cell lines, as control cell culture lines without virus were also
exposed to tea tree oil. The degree and extent of the antiviral activity
of tea tree oil was determined. In addition, the major individual components
of tea tree oil were assessed to identify the components of tea tree oil
responsible for the antiviral activity. Following in vitro testing,
collaboration with industry resulted in the formulation of a product suitable
for the topical treatment of coldsores and this product was evaluated in
a pilot study. |
|
Outcomes
|
This
project has established that tea tree oil and several of its components
have activity against herpes simplex viruses in vitro. It has also
established that tea tree oil may be a potentially efficacious treatment
for coldsores, a cutaneous herpes infection. Based on the promising results
from this pilot study, another larger study is underway. |
|
Implications
|
Confirmation
of the in vitro antiviral activity of tea tree oil complements the
well-established antibacterial and antifungal activity. It adds another
dimension to the profile of this essential oil and should enhance future
marketing approaches. Furthermore, if the efficacy of tea tree oil products
for the treatment of cold sores is confirmed by others, the tea tree oil
industry will have access to a massive world-wide market. |
|
Publications
|
A
manuscript reporting the in vitro activity of tea tree oil against
herpes simplex virus is in preparation. A short report describing the results
of the pilot study has been accepted for publication in a peer-reviewed
medical journal:
Carson, C. F., Ashton, L.,
Dry, L., Smith, D. W. & T. V. Riley. 2001 Melaleuca alternifolia
(tea tree) oil gel (6%) for the treatment of recurrent herpes labialis.
Journal
of Antimicrobial Chemotherapy in press. |
|
Project
Title:
|
The
antifungal activity of tea tree oil |
|
RIRDC Project No.:
|
UWA-50A |
|
Researcher:
|
KA
Hammer, CF Carson, TV Riley |
|
Organisation:
|
Department
of Microbiology, The University of Western Australia, and
The Western Australian Centre
for Pathology and Medical Research |
|
Phone:
|
08
9346 3690 |
|
Fax:
|
08
9346 2912 |
|
Email:
|
triley@cyllene.uwa.edu.au |
|
Objective
|
To
expand the acceptability of tea tree oil as a naturally occurring antifungal
agent by determining the in vitro susceptibility of a large number
of fungal isolates to tea tree oil. |
|
Background
|
Previous
research projects have demonstrated that tea tree oil has a broad range
of antibacterial activity, however, little data has been generated regarding
the antifungal properties of the oil. This area of research needs urgent
attention to bolster the acceptability and scientific credibility of the
oil. The most important organisms to test are those causing infections
that are amenable to topical treatment. This includes yeasts such as Candida
and
the filamentous fungi comprising the group known as the dermatophytes (Trichophyton,
Epidermophyton
and Microsporum). |
|
Research
|
The
first major objective was to develop an appropriate in vitro susceptibility
testing method, as susceptibility testing of fungi is not well developed.
Broth and agar dilution methods were investigated for their suitability.
The second major objective was to obtain reference strains of fungi and
determine their susceptibility to tea tree oil. Minimum inhibitory concentrations
(MICs) and minimum fungicidal concentrations (MFCs) were determined for
these isolates. |
|
Outcomes
|
Results
of the broth microdilution method showed that the yeast isolates (including
members of the genera
Candida, Cryptococcus, Rhodotorula, Saccharomyces
and
Trichosporon) were inhibited by tea tree oil in the range of 0.03%
to 0.5%, and were killed by tea tree oil in the range 0.06% to 1.0%. Similarly,
results for the dermatophytes obtained by the broth microdilution method
showed that they were inhibited in the range of 0.004% to 0.03% and were
killed in the range of 0.06% to 1.0%. |
|
Implications
|
The
data generated in this project demonstrates that both yeasts and dermatophytes
are susceptible to tea tree oil. This provides the basic information required
to then develop and finally evaluate tea tree oil products for the treatment
of fungal infections. |
|
Publications
|
KA
Hammer, CF Carson, TV Riley. 1999. In vitro susceptibility of yeasts
to Melaleuca alternifolia
(tea tree) oil. Proceedings of the IXth
Congress of Bacteriology and Applied Microbiology and the IXth International
Congress of Mycology (Poster and Abstract) 16-20th August, 1999, Sydney,
Australia.
KA Hammer, CF Carson, TV
Riley. 2000. Activity of Melaleuca alternifolia (tea tree) oil against
dermatophytes in vitro. Proceedings of the Joint Annual Scientific
Meeting and Exhibition of ASM, NZMS and FAPMS, (Poster and Abstract) 8-13th
July, 2000, Cairns, Australia. |
|
Project
Title:
|
Skin
sensitivity testing for tea tree oil - second stage |
|
RIRDC Project No.:
|
UWA-51A |
|
Researcher:
|
A/Prof
T. Riley |
|
Organisation:
|
University
of Western Australia
Dept of Microbiology
Queen Elizabeth II Medical
Centre
Nedlands
WA 6009 |
|
Phone:
|
08
9346 3690 |
|
Fax:
|
08
9346 2912 |
|
Email:
|
triley@cyllene.uwa.edu.au |
|
Objective
|
To
further assess skin sensitivity to and safety of tea tree oil and its major
components. |
|
Background
|
Current
safety information about tea tree oil in the biomedical literature is mainly
in the form of short reports about adverse cutaneous reactions to the oil.
This pattern of reporting does not provide an overall picture of the prevalence
of adverse events to tea tree oil in the general population. The previous
RIRDC-sponsored skin sensitivity project determined that approximately
2% of a non-dermatology self-selected population had positive patch tests
to tea tree oil, however, more detailed information was required. In addition,
poisoning due to ingestion of tea tree oil has been reported infrequently,
however, the true prevalence of tea tree oil poisoning is not known. |
|
Research
|
Volunteers
with a known allergy to tea tree oil were sought and tested with 12 components
of tea tree oil at concentrations approximating those found in pure tea
tree oil: terpinen-4-ol (40%), a -terpinene (25%), g -terpinene (10%),
aromadendrene (5%), 1,8-cineole (5%), r -cymene (5%), a -pinene (5%), a
-terpineol (5%), terpinolene (5%), limonene (1%), a -phellandrene (1%)
and viridiflorene (1%). Eight volunteers with confirmed allergy to tea
tree oil were patch tested to the components. Investigations of the stability
of tea tree oil and the influence of storage conditions were conducted
in this project. One batch of tea tree oil was exposed to a range of storage
conditions using the variables of light, air and temperature. A survey
of tea tree oil poisoning was conducted. |
|
Outcomes
|
The
results suggest that oxidation products of tea tree oil, rather than individual
components of fresh tea tree oil, are responsible for allergic reactions.
Exposure to light and/or air accelerated the production of oxidation products
in tea tree oil. Based on a retrospective collection of data from Poisons
Information Centres around Australia, poisoning events are relatively common.
Most occur in the very young (2 years of age or less).
|
|
Implications
|
Storage
and sale of pure oil in dark bottles is recommended. It may be necessary
to reduce the oil shelf life once bottles have been opened. Poisonings
could probably be prevented by having child-proof caps on all bottles of
pure oil. |
|
Publications
|
Two
articles have been accepted for publication:
Greig, J.E., Thoo, S-L.,
Carson, C.F. and Riley, T.V. (1999) Contact sensitivity to a tea tree oil
product not due to tea tree oil. Contact Dermatitis 41:354-355.
Greig, J.E., Carson, C.F.,
Stuckey, M.S. and Riley, T.V. (2000) Prevalence of contact sensitivity
to the European standard series in a self-selected population. Australasian
Journal of Dermatology41:86-89.
Another manuscript is in
preparation for submission to a peer-reviewed international biomedical
journal. |
|
Project
Title:
|
Development
of DNA markers for tea tree |
|
RIRDC Project No.:
|
CSF-55A |
|
Researcher:
|
Dr
John Doran & Dr Gavin Moran |
|
Organisation:
|
CSIRO
Forestry & Forest Products
PO Box E4008
KINGSTON ACT 2604 |
|
Phone:
|
02
6281 8211 |
|
Fax:
|
02
6281 8266 |
|
Email
|
John.Doran@ffp.csiro.au
Gavin.Moran@ffp.csiro.au |
|
Objective
|
To
develop a dinucleotide microsatellite DNA library for tea tree and to characterise
10 microsatellite loci. The most useful microsatellite loci and primer
sequences for fingerprinting breeding lines identified by this research
will be documented in a Commercial-in-Confidence report to the RIRDC /ATTIA
Tea Tree Breeding Project meeting of August 2000. |
|
Background
|
DNA
markers provide a means of monitoring pollen flow and assessing the level
of contamination in seed orchards, testing the validity of controlled crosses,
of identifying selfs and fingerprinting clones. The study of genetic segregation
in full-sib progenies allows genetic linkage maps to be constructed. These
maps provide a framework in which genes of economic or practical significance
can be located. The RIRDC/ATTIA tea tree breeding project will produce
the first highly improved seed from its orchards in 2000. Unrestricted
access to its own DNA markers, as provided by this project, to monitor
the distribution and use of this seed and any clones released by the project
will be a powerful deterrent to the misuse of this material, vital to the
future of the industry in Australia. |
|
Research
|
Twenty-three
microsatellite loci have been characterised in Melaleuca alternifolia.
These microsatellites have been grouped into 6 multiplexes for efficient
use in applications in the breeding program. The microsatellites showed
mendelian segregation in controlled crosses. The eight parental breeding
clones were typed for their DNA genotypes at the loci and could be distinguished
from each other on the genotypes on the just the first two loci. These
genotypes were used to certify ramets against ortets of several other breeding
clones and some ramets were found to be incorrect. |
|
Outcomes
|
Twenty-three
microsatellite loci are now available for use in the breeding of M.
alternifolia.
DNA fingerprinting of ramets
of breeding clones has revealed errors in labelling ramets used in a breeding
arboretum, confirming the value of the technique in quality control.
The assays of progeny from
controlled crosses without emasculation have shown that significant levels
of selfed seed can occur. This needs to be tested across a number of females. |
|
Implications
|
Microsatellites
can now be used to routinely to monitor for quality control in the breeding
program. Production of selfed seed in controlled crosses without emasculation
suggests that this method may have limited application in breeding programs. |
|
Publications
|
Commercial-in-Confidence
report to RIRDC/ATTIA Tea Tree Breeding Committee |
|
Project
Title:
|
Plant
Nutritional Survey of the Australian Tea Tree Industry |
|
RIRDC Project No.:
|
DAQ-252A |
|
Researcher:
|
James
Drinnan |
|
Organisation:
|
Queensland
Department of Primary Industries
PO Box 1054
MAREEBA QLD 4880 |
|
Phone:
|
07
4092 8555 |
|
Fax:
|
07
4092 3593 |
|
Email
|
DrinnanJE@dpi.qld.gov.au |
|
Objectives
|
·1 Determine the
current nutritional status and corresponding yields of tea tree grown in
Australia (North Queensland and Northern New South Wales).
·2 Determine some
ballpark optimum fertiliser recommendations for tea tree.
·3 Improve the knowledge
base of the Australian producers on the nutritional requirements of tea
tree.
|
|
Background
|
The
Australian tea tree industry is likely to face strong competition from
low cost overseas producers in the near future. Also, unless the demand
for tea tree oil continues to increase rapidly to meet increasing supply
there is likely to be pressure on the price of tea tree oil. Given these
circumstances, producers must reduce their costs of production. One area
highlighted by RIRDC (98/99 key issue) and the Australian Tea Tree growers
association to help achieve this is to determine the nutritional requirements
for maximising yields. In high production areas such as north Queensland
- where water, temperature and radiation are not limiting and soils are
relatively infertile, and in NSW on less fertile soils or where soil fertility
has declined (due to a number of cropping cycles), nutrition is considered
one of the major limitations to increased yields. By conducting this nutritional
survey the range in types and amounts of fertiliser being used and the
relationship with yields can be assessed. |
|
Research
|
A
survey was conducted of growers in QLD and NSW to determine current fertiliser
practices (types and quantities) and the biomass and oil yields achieved.
Leaf and soil analysis results were collected, collated and analysed. Information
on soil type and fertility, irrigation levels, leaf drop and plant size
at harvest was also collected. An estimate of fertiliser requirement was
made by calculating nutrient removal in the biomass. |
|
Outcomes
|
This
project has increased the knowledge base of the nutritional requirements
of tea tree. The survey has documented the current nutritional status of
the Australian Tea Tree Industry. While the survey indicated little correlation
between fertiliser inputs and oil yield, this may be due to the variety
of factors which influence yield. However, a conservative approach and
one which will apply in the long term is to use sufficient fertiliser to
replace the nutrients removed at harvest. Results have indicated the amounts,
types and timing of fertiliser being used and the range in yields being
achieved. The optimal leaf and soil nutrient levels established provide
a guide for growers to assess their fertiliser practices. From nutrient
removal calculations it is recommended growers in QLD use around 180 kg
N, 20 kg P and 220 kgK/ha/year and in NSW 130 kg N, 15 kg P and 158 kgK/ha/year.
This should be applied regularly in small amounts throughout the growing
season in approximately the following proportions - 10% from 0-2, 20% from
2-4 months, 20% from 4-6 months following harvest and 50% from 6 months
after harvest until the trees are harvested again. |
|
Project
Title
|
Skin
sensitivity testing for tea tree oil |
|
RIRDC Project No.:
|
UWA-42A |
|
Researchers:
|
Dr
J E Greig, Ms C F Carson, Dr M S Stuckey, A/Prof T V Riley |
|
Organisation:
|
Department
of Microbiology, The University of Western Australia
and Division of Microbiology
and Infectious Diseases, PathCentre
Queen Elizabeth II Medical
Centre,
NEDLANDS WA 6009 |
|
Phone:
|
08
9346 3690 |
|
Fax:
|
08
9346 2912 |
|
Email:
|
triley@cyllene.uwa.edu.au |
|
Objective
|
To
evaluate the ability of tea tree oil and its major components to cause
skin sensitivity. |
|
Background
|
For
almost 80 years, tea tree oil has been marketed as a safe and efficacious
topical antimicrobial agent. While there is sufficient scientific evidence
showing its antimicrobial properties in vitro, data supporting its
safety remain limited, fragmented and largely anecdotal. Although adverse
reactions appear to occur relatively infrequently, a number of cases of
contact dermatitis to tea tree oil have been reported. Yet there is little
information available regarding the frequency and reasons for these allergic
or irritant reactions. |
|
Research
|
The
research involved testing over 200 healthy volunteers for allergy to tea
tree oil using two different tests. Ten tea tree oils were tested to determine
whether there would be any difference in reactions.
The prick test involves an
immediate allergic reaction. It is the type of test used in the diagnosis
of grass and dust-mite allergy amongst other things, and we tested these
allergens as well as tea tree oil in order to determine if our volunteer
population was more or less allergic than average.
The patch test detects a
delayed reaction that develops on the skin surface. It is used to diagnose
allergic contact dermatitis, but sometimes causes an irritant reaction.
There are some substances that commonly cause allergic dermatitis.
We tested the volunteers
to some of these in addition to tea tree oil in order to determine their
overall reactivity in this type of test. Any volunteer who exhibited a
reaction to tea tree oil was tested again with 100% oil, 10% oil and oil
components. |
|
Outcomes
|
The
volunteers ranged in age from 18 to 82 years, with an average age of 40.
Women made up 61% of the group, and 63% of volunteers were sure of having
previously used tea tree oil.
The tests for immediate allergy
indicated that while we had an overly reactive group of people, only 1.4%
of people (3 of 219) displayed any reaction to tea tree oil, and reactions
were to only 1 or 2 of 10 oils.
The volunteers also appeared
to be slightly more reactive to contact allergens than might be expected.
A total of 52 of the 219 volunteers displayed some reaction to tea tree
oil although, in a number of these people, this consisted only of a questionable
reaction to 1 or 2 of the 10 oils. Secondary testing was performed on 33
volunteers. Results were classified as allergic contact dermatitis, mild
or marked irritant contact dermatitis, indistinguishable between allergy
and irritancy, or no response.
The prevalence of allergy
in the whole group was 2.9% up to a possible 4.8% if indistinguishable
is included. To have an allergy requires a previous exposure to the substance
being tested, and the levels of allergy amongst those who had previously
used tea tree oil was 4.6% up to a possible 7.6% including the indistinguishable
reactions. The prevalence of marked irritancy to 100% tea tree oil ranged
from 2.4-4.3% (with or without the indistinguishable reactions), with any
level of irritancy ranging from 7.2-10.1%. Irritant reactions are particularly
concentration dependent, which means that many of these reactions should
be avoidable if a lower concentration of oil is used. Very few reactions
occurred in response to tea tree oil components, with a single mild response
to each of 2 components, and 4 significant reactions to another component. |
|
Implications
|
While
the prevalence of irritant or allergic reactions to tea tree oil is low,
it is clear that a small proportion of people may experience adverse effects,
especially if 100% oil is used. This information will allow appropriate
marketing of the product for safe usage. |
|
Project
Title
|
The
antimicrobial activity of tea tree oil |
| RIRDC
Project No.: |
UWA-24A |
|
Researcher:
|
Assoc.
Professor T. V. Riley |
|
Organisation:
|
Department
of Microbiology
The University of Western
Australia
Queen Elizabeth II Medical
Centre
NEDLANDS WA 6009 |
|
Phone:
|
08
9346 3690 |
|
Fax:
|
08
9346 2912 |
|
Background
|
Despite
the increasing interest in tea tree oil for therapeutic purposes, the vast
majority of reports of its efficacy in treating a variety of infections
are anecdotal and there is a paucity of information in appropriate peer-reviewed
journals. This situation constitutes a significant dilemma for the tea
tree oil industry. Early submissions to the Food and Drug Administration
in the United States of America for tea tree oil to be registered as an
over-the-counter topical antimicrobial have not been successful. One reason
for this is that published
in vitro efficacy data were lacking. |
|
Research
|
Adequate
data regarding the susceptibility of various pathogens to tea tree oil
are required. Therefore, one of the first priorities was to accumulate
substantial data on isolates from infections potentially treatable with
tea tree oil. In addition, investigations into the antimicrobial activity
of the individual components were required. The second area of research
was a focus on the mechanism of action of tea tree oil, as no information
on this area was available. |
|
Outcomes
|
As
a first step, methods were developed and validated and finally, a broth
micro-dilution method was used to examine the susceptibility of various
bacteria. All bacteria tested were susceptible to tea tree oil with only
one, Pseudomonas being slightly less susceptible. For example, methicillin-resistant
strains of
S. aureus (MRSA), an important cause of hospital-acquired
infections was inhibited by 0.25% tea tree oil suggesting tea tree oil
may be useful in the treatment of MRSA. Other studies indicated that tea
tree oil, when formulated into appropriate products, may be useful in the
treatment of bacterial vaginal infections. The antimicrobial activity of
eight components of tea tree oil was evaluated using disc diffusion and
broth microdilution methods. Terpinen-4-ol was active against all the test
organisms while r -cymene demonstrated no antimicrobial activity. Linalool
and a -terpineol were active against all organisms with the exception of
Pseudomonas.
The Food and Drug Administration
requires that the in vitro antimicrobial spectrum of compounds intended
for use as a health-care antiseptic be determined. We therefore tested
a range of normal and commensal isolates of the type found on skin. The
result suggested that tea tree oil may be useful in removing transient
skin flora while suppressing but maintaining resident flora.
Treatment of E. coli
suspensions with tea tree oil or components resulted in significant reductions
in optical density. These results suggested that the membrane was a site
of action in E. coli. Other experiments showed that genetic material
was being lost from bacterial cells through damage to the membrane. C.
albicans cells were not lysed with terpinen-4-ol treatment and by electron
microscopy, appeared unaltered. In contrast, E. coli cells appeared
as empty "ghost" cells by electron microscopy. The appearance of terpinen-4-ol
S.
aureus also suggested damage to the cell membrane or wall. The original
premise, that tea tree oil and/or its components act on the cell membrane
or wall, was confirmed. While further evidence is required to corroborate
these observations, the possibility that other sites of action may exist,
must be considered. |
|
Implications
|
This
project has firmly established that tea tree oil has significant antimicrobial
activity. The results have been published in mainstream medical and scientific
journals and generated considerable interest in Australia and, in particular,
Europe and the United States. The industry now has a firm basis for the
next step in the promotion of tea tree oil as a bona fide topical
antibiotic. This is to establish that tea tree oil products work in the
clinical setting. To do this randomised clinical trials will need to be
conducted at appropriate testing centres. This is an expensive exercise,
however, the potential benefits to the industry should justify the outlay. |
|
Project
Title
|
Herbicides
for weed control in tea tree oil plantations |
|
RIRDC Project No.:
|
DAN-74A |
|
Researcher:
|
Tony
Cook |
|
Organisation:
|
NSW
Agriculture
Tamworth Centre for Crop
Improvement
Calala Lane
TAMWORTH NSW 2340 |
|
Phone:
|
02
6763 1100 |
|
Fax:
|
02
6763 1222 |
|
Objectives
|
To
develop effective herbicidal weed control practices for Australian tea
tree oil plantations and ensure new herbicide recommendations do not affect
quality of oil. |
|
Background
|
Tea
tree oil is extracted from an Australian native species Melaleuca alternifolia.
Weed control is considered the major problem by growers. In 1990, there
were only four legalised herbicide treatments available and subsequently
left growers with very expensive and limited weed control options. In addition,
there is a need to maintain high production and quality of tea tree oil.
Clearly there will be a need to guarantee any new recommended treatments
do not contaminate the oil with herbicide residues. |
|
Research
|
A
survey was conducted to determine the major weed species and the techniques
used to control these weeds. In addition, 65 herbicides were screened for
a range of tea tree growth stages, in order to identify treatments that
were safe to tea tree, provided adequate weed control and were not too
cost prohibitive. |
|
Outcomes
|
Approximately
80% of growers surveyed stated that weeds are a major limitation to production
and half were dissatisfied with their current weed control techniques.
The five most abundant weeds were kidney weed (Dichondra repens),
carpet grass (Axonopus affinis), sedges (Cyperus spp.) fleabane
(Conyza spp) and couch grass (Cynodon dactylon). It was shown
that the majority of competition from weeds occurred in the first month
after planting. A 97% reduction in yield was a consequence of high weed
densities in the first few months after planting.
There are now eighteen registered
treatments with all but one being Pesticide Order treatments. In some cases,
recommended treatments arising from this project are 80% cheaper that previously
recommended treatments and exhibit little difference in weed control and
safety. There was no detectable level of herbicide residue in oil samples
from tea trees treated with some of the new recommended treatments.
A weeds identification and
weed control booklet will transfer information gained from this project
to relevant people and will be published in 1996. |
|
Implications
|
A
minimum of $1,100 per hectare can be returned to growers in weedy situations
by adopting the results of this project. Apart from these financial gains,
new recommendations will allow for increased managerial choices, superior
weed control and less likelihood of developing herbicide resistance.
Growers will possess better
weed identification skills as a result of the advisory booklet and will
be best advised to solve a particular weed problem.
Although considerable cost
savings were made with new treatments (blanket applied), there are further
savings and benefits if the practice of directed spraying was properly
developed. This could allow the use of herbicides normally damaging to
tea trees. |
|
Project
Title
|
Insect
pest management in tea tree |
|
RIRDC Project No.:
|
DAN-91A |
|
Researchers:
|
Mr
Gus Campbell |
|
Organisation:
|
NSW
Agriculture
PO Box 72
ALSTONVILLE NSW 2477 |
|
Phone:
|
02
6628 0604 |
|
Fax:
|
02
6628 5209 |
|
Objectives
|
To
develop an effective sustainable pest management strategy for the Pyrgo
beetle and other pests of tea tree by:
· correlating the
incidence of Pyrgo in the field with weather parameters, and refining the
maximum temperature threshold values for larval and egg survival to account
for field observations and to improve predictive modelling;
· evaluating a monitoring
procedure for detecting Pyrgo in the field; and
· screening selected
insecticides and other chemicals for efficacy against Pyrgo in the laboratory
and the field.
|
|
Background
|
The
tea tree industry of northern NSW and southern Queensland has developed
over the last 20 years from a fledgling cottage industry into a substantial
producer of some 260 tonnes of tea tree oil per annum. The early industry
was based on bush harvesting but has now progressed to one of plantation
culture using improved cultivars on more than 4,000 ha. Although the industry
faces a number of problems, one of the more important affecting production
is caused by a number of insect pests - the major one being Pyrgo beetle.
Insect problems are recognised
and acknowledged by most growers, but little is known about the ecology
of Pyrgo, and this has limited the development and implementation of appropriate
control strategies. The industry has been promoted as being "clean and
green", implying minimal or no use of insecticides, but this is belied
by the substantial evidence (residues in the oil) showing that unregistered
insecticides have been used on many crops. This is partly caused by the
paucity of insecticides (only one is registered for use in NSW) legally
available to growers, and there is clearly the need for a range of products
to be available for use.
If rational insect control
strategies are to be developed and implemented for the industry, then it
is important to have a better understanding of the ecology of the pests
concerned. Once this is established, potential insecticide and other control
measures can then be devised and evaluated. |
|
Research
|
Considerable
field and laboratory research has been undertaken over the last three years
to investigate the various factors which, collectively, result in loss
of foliage and oil production. These have included studies on the ecology
of the insects concerned, on the development of systems for monitoring
the first occurrence and incidence of insects in plantations, on screening
cultivars for insect resistance, and on evaluating a range of insecticides
and other chemicals for potential use in chemical control strategies. This
latter activity was instigated part of the way through the project, when
insecticide residues were detected in oil - from crops clearly treated
(illegally) with insecticides not registered for the purpose. |
|
Outcomes
|
There
is now an excellent understanding of the ecology of Pyrgo and some of the
other insects which also cause yield losses. A practical monitoring system
based on sticky yellow traps has been developed and this will allow the
more rational application of control strategies including the reduction
in use of insecticide treatments. Several alternative insecticides have
been evaluated, and been shown to provide more effective control than the
current sole product (methomyl). |
|
Implications
|
Growers
now have a better understanding of the population dynamics of Pyrgo, and
of the importance of other insect pests such as mites and psyllids. With
the development of improved monitoring using sticky yellow traps, there
is now the opportunity to detect the presence of Pyrgo earlier than on-plant
inspections, to allow the identification of localised areas of beetle activity,
and to reduce insecticide costs by rationalising their use. There may be
an added opportunity for the industry to employ scouts to undertake this
monitoring and to advise growers on the need to use insecticide treatments.
Illegal use of non-registered
insecticides is a potential "time bomb" that, if not addressed quickly,
will seriously harm the industry. Several potential insecticide products
have been evaluated and found to be more effective than the current permitted
product, methomyl. Steps should be taken urgently to secure their registration
for use on tea tree.
This project has highlighted
the need for further research on control of mites and psyllids, and on
the screening of insecticides to determine their potential for leaving
residues in oil. |
|
Project
Title
|
Towards
non-chemical control of weeds in tea tree |
|
RIRDC Project No.:
|
US-20A |
|
Researchers:
|
Dr
BG Sutton, Dr RD Cousins and Dr J Murtagh |
|
Organisation:
|
University
of Sydney
GOONELLABAH NSW 2480 |
|
Phone:
|
02
9692 2050 |
|
Fax:
|
02
9692 4172 |
|
Objectives
|
· To survey tea
tree growers to establish the range of weed problems encountered, and the
scope of current weed control techniques used in tea tree cultivation.
· To identify the
mechanisms by which weeds inhibit the growth and oil production of established
tea tree plantations.
· To define practical
methods of weed control for plantation managers, which minimise the use
of herbicides.
|
|
Background
|
The
perception of the tea tree industry is that weeds inhibit plantation production
in two phases - establishment and regrowth.
The extent to which weeds
affect the regrowth of tea tree by competing for light, nutrients and water
has not been quantified, but the industry perception is that it is a real
but variable problem. It is postulated that weed problems are linked to
loss of fine roots of tea tree following coppicing. In these situations,
the tea tree plant has weakened competitive ability against rapidly growing
annual weeds until regrowth has been well established. The use of herbicides,
as is currently practiced, is seen as damaging to the image of the product
(tea tree oil), by growers and potential consumers. A range of cultural
practices additionally used by growers, could form the basis of a non-chemical
system of weed control in plantations.
This study seeks to evaluate
these alternatives. The information gained should provide guidance on when
weed control is required during the regrowth cycle, and what the method
used must achieve if it is to be successfully adopted. |
|
Research
|
A
wide range of pot and field experiments were conducted to provide more
information on the nature of root and top growth in coppiced tea trees,
to allow a better understanding of the physiology of the crop in competition
with weeds at different stages of its regrowth. The response to nitrogen
nutrition was also examined.
Concurrently, other studies
were undertaken to determine the effectiveness of various weed control
strategies such as herbicide use (overall and strip treatments), cover
crops, mowing, mechanical cultivation, and hand hoeing. These trials were
undertaken at several localities over a three year period. |
|
Outcomes
|
The
results of these studies showed that weeds reduced tea tree leaf yields
by an average 27% (range 9 to 47), but without affecting oil concentration
or quality. This loss in yield is associated with competition for light,
water and nutrients (especially nitrogen).
Two features of the regrowth
cycle of tea tree are thought to be relevant to the crop’s competitiveness
after harvest: the first, "coppice vigour" (the high relative growth rate
of new shoots from the cut stump) increases the crop’s ability to compete
for light; while the second, death of fine roots about halfway through
the regrowth cycle, reduces the crop’s ability to compete for water and
nutrients in the latter half of the regrowth cycle.
When all weed control strategies
were compared, herbicides continued to provide the most effective control,
while mechanical cultivation was the best of the non-chemical methods.
Other strategies used by the industry may also be effective, but they need
to be assessed against these two standards. |
|
Implications
|
While
the use of herbicides still provides the most effective method of weed
control, non-chemical methods can also be used but, irrespective of the
method selected, it is imperative that it be implemented in the latter
half of the regrowth cycle when competition from weeds is greatest. |
|
Project
Title
|
Breeding
and selection of Australian tea tree for improved oil yield and quality |
|
RIRDC Project No.:
|
DAN-87A |
|
Researchers:
|
John
Murtagh #9; Gary Baker John Doran |
|
Organisation:
|
Agric.
Water Man. #9; NSW Agriculture CSIRO
Wollongbar Ag. Inst. PO Box
E4008
WOLLONGBAR KINGSTON
NSW 2477 ACT 2604 |
|
Phone:
|
02
6626 1104 02 6281 8319 |
|
Fax:
|
02
6628 3264 02 6281 8266 |
|
Email:
|
bakerg@agric.nsw.gov.au
John.Doran@ffp.csiro.au |
|
Objective
|
To
select and breed seed for economic gains in oil characteristics. Gains
in yield and quality are considered essential if the Australian tea tree
industry is to prosper against overseas competition and the downward pressure
on oil prices. |
|
Background
|
The
Australian tea tree industry has developed from bush production to plantation
production. Seed for planting is collected from natural populations using
only rudimentary selection to ensure that oil quality meets industry standards.
The yields of oil from plantations are variable; there is much scope to
improve both the amount and quality of the yield. |
|
Research
|
During
the first three years of the project (1993-1996), seven field trials were
established to determine the genetic variability in oil yield and quality.
Two of these trials were then developed as seed orchards to provide improved
seed to the industry. A natural stand of 783 trees was sampled, trees were
analysed and ranked for oil concentration, terpinen-4-ol and cineole. Selecting
the best 74 trees for seed production provides a selection pressure of
>1:10. This ratio will enable genetic gain for selected traits.
A progeny trial of 204 families
will be further tested for oil characteristics, superior trees selected
and inferior trees culled to prevent them breeding with superior trees.
The superior trees will grow on and flower to produce genetically improved
seed. The coppicing ability of families grown at different sites will also
be used to select superior families in the orchard. |
|
Outcomes
|
Variation
of key commercial traits were significant at the provenance, family and
individual tree levels. Heritability (narrow sense) was high (0.51) for
oil concentration, moderate (0.37) for cineole% and low for the growth
parameters of plant height (0.21) and stem diameter (0.14). No adverse
genetic correlations were found between oil concentration and plant height
and diameter.
The performance of families
across two sites (family x site interaction) was reasonably consistent,
indicating that it will be possible to select families with good general
adaptability in a single breeding population, thus avoiding the extra cost
of establishing multiple breeding populations in different environments.
The best performing provenances
were identified and seed from these areas will be released to the industry.
The controlled pollinations in 1995 have produced seeds, indicating that
the methodology used has potential. |
|
Implications
|
All
the indicators from the first phase of breeding point to very substantial
economic gains being achieved by the breeding project. Three years is a
very short time in tree breeding and more time is needed to produce the
much improved seed required to ensure the successful development and survival
of this industry. |
|
Publications
|
Doran,
J. C. (1995). Estimating seed quantities for tea tree plantations.
Australian Tea Tree Industry Association Newsletter, April 1995.
Doran, J. C., Baker, G. R.,
Murtagh, G. J. Williams, E. R. and Morris, S. G. (1996). "Breeding and
selection of Australian Tea Tree for improved oil yield and quality 1993
to 1996" Review Report for the Rural Industries Research And Development
Corporation and the Australia Tea Tree Industry Association.
Doran, J. C., Baker, G. R.,
Murtagh, G. J. and Southwell, I. A. (1996). "Breeding and selection
of Australian Tea Tree for improved oil yield and quality" Final Report
for Rural Industries Research And Development Corporation. |
|
Project
Title
|
Significance
of cineole for the bioactivity and irritancy of tea tree oil |
|
RIRDC Project No.:
|
DAN-104A |
|
Researcher:
|
Dr
Ian Southwell |
|
Organisation:
|
NSW
Agriculture
Wollongbar Institute
WOLLONGBAR NSW 2477 |
|
Phone:
|
02
6626 1224 |
|
Fax:
|
02
6628 3264 |
|
Objective
|
To
increase the market demand for tea tree oil by measuring and documenting
data on the skin irritancy and minimum inhibitory concentrations (MICs)
of different grades of tea tree oil that might be required by regulatory
bodies like the USFDA for monograph acceptance. |
|
Background
|
Approximately
200 tonnes of tea tree oil, valued (farm gate) at $10m, are currently produced
in Australia per annum. The product is used as an antimicrobial antiseptic
oil or formulated into value added creams, shampoos, soaps, mouthwashes,
toothpastes etc. A significant rural industry is being established around
the propagation, production, processing, formulation and marketing of tea
tree, the oil and its products. Plantations are expected to yield 400 tonnes
pa by the late 1990s.
However, one factor hindering
the broadening of the tea tree oil market base is that oil reach in cineole
is considered to be of high skin irritancy and therefore not of a marketable
standard. |
|
Research
|
Standard
clinical procedures were used to test cineole and tea tree oil for skin
irritancy. Twenty five human subedits were subjected to occlusive patch
testing applied to the upper arm or back for five days per week for three
consecutive weeks. The patch was removed at 24 hour intervals and any skin
reaction noted. Subjects reacting allergically to the test substances were
withdrawn from the irritancy trial and were used in further testing for
allergic reaction to individual components or fractions.
More than 20 strains of bacteria
were used to test numerous tea tree oils with varying levels of cineole
concentration for antimicrobial activity. |
|
Outcomes and Implications
|
The
results of this research have major implications for the industry. Some
years ago, oils with 5-10% cineole were perfectly acceptable in the marketplace.
In recent years though, buyers have been seeking oils with less than 5%
and sometimes less than 3%.
This research shows clearly
that there are no grounds for promoting low cineole oils other than for
avoiding low terpinen-4-ol oils. If all buyers could be convinced of this,
more tea tree oil could be offered for sale, providing a yield boost to
many producers.
The results of the project
should aid the marketing of tea tree oil. It documents: 1) the absence
of skin irritancy for formulated preparations; 2) the non-allergenic nature
of most tea tree oil constituents; 3) methods for the removal of some possible
allergens; 4) a wider range of tea tree oil-susceptible microorganisns;
5) specific MIC values for a range of oils; and 6) enhanced MIC values
for specific oils. |
|
Project
Title
|
Developing
the North Queensland tea tree industry |
|
RIRDC Project No.:
|
DAQ-184A |
|
Researcher:
|
James
Drinnan |
|
Organisation:
|
Queensland
Department of Primary Industries
PO Box 1054
MAREEBA QLD 4880 |
|
Phone:
|
07
4092 8555 |
|
Fax:
|
07
4092 3593 |
|
Objectives
|
· To facilitate
the rapid development of the knowledge base on the production of tea tree
oil in the Mareeba Dimbulah Irrigation Area, Qld.
· To develop guidelines
for irrigation scheduling for maximising oil yield and quality.
· To establish a gene
pool of selected superior plants.
|
|
Background
|
Tea
tree oil production is a relatively new industry on the Atherton Tablelands
in North Queensland. Interest in tea tree oil production was generated
as an alternative crop for tobacco. The production systems being used now
are based on New South Wales information, use high densities, and are irrigated.
Due to differences in climate and soil types it is essential to adapt the
findings from New South Wales research work for North Queensland conditions.
Environmental and management effects, particularly irrigation, look to
have a major impact on oil yields. |
|
Research
|
Information
on tea tree production has been gathered from key researchers working with
tea tree. A soil moisture monitoring system (Environscan) has been used
to investigate water use and water requirements of tea trees in North Queensland.
Data has been collected on oil quality and quantity and the factors affecting
it. Several seedlings have been identified as having superior oil concentration
and quality. Superior planting material has also been sourced from the
tea tree breeding program and is being evaluated at two locations in the
Mareeba Dimbulah Irrigation Area. |
|
Outcomes
|
Information
was presented to growers via field days, newsletters, progress reports,
presentations at growers' meetings and farm visits.
Irrigation scheduling guidelines
have been developed. Mature trees use 0.8-1.0 times the pan evaporation
rate which is equivalent to a total water requirement of I OML/ha/year
or 7.5ML/ha/year when rainfall is subtracted.
Major factors influencing
oil concentration and hence yields identified include genotype, time of
year, nutrition, irrigation, and seedling vs coppice growth. |
|
Implications
|
This
project has helped with the very successful development of the North Queensland
tea tree oil industry. There has been a rapid expansion of the industry
and yields and oil quality has been excellent. |
